The overall goal of this research is to delineate the mechanisms which regulate signal transduction by the neurally active cytokines, leukemia inhibitor factor (LIF) and ciliary neurotrophic factor (CNTF). LIF and CNTF use an overlapping set of receptor polypeptides: LIF action is mediated by a heterodimeric receptor consisting of the low affinity LIF receptor (LIFR) and gp130, and CNTF uses a receptor consisting of LIFR, gp130, and the (nonsignaling) low affinity CNTF receptor. LIF and CNTF are members of a family of pluripotent cytokines that can regulate both neuronal survival and phenotypic expression of neuropeptides and neurotransmitters. The specific aims of this proposal are: (l) To determine the mechanisms responsible for the regulation of LIF receptor signaling by mltogen-activated protein kinase (MAPK). We have found that the LIFR is phosphorylated by MAPK after stimulation of cells with LIF or other growth factors. Removal of the MAPK phosphorylation site eliminates the ability of heterologous receptor activation to regulate LIFR-mediated induction of gene expression. This proposal will determine the molecular and cellular mechanisms responsible for the regulation of neurokine signal transduction by MAPK-mediated phosphorylation of the LIFR. (2) To determine the functional consequences of LIF-stimulated serine phosphorylation of gp130, and to identify the kinase responsible for this phosphorylation. We have demonstrated that gp130 is rapidly serine phosphorylated by an unknown kinase after stimulation with LIF. The site of phosphorylation is adjacent to a dileucine sequence previously shown to be involved in receptor internalization. We will determine the role of this phosphorylation in LIF-mediated signal transduction and receptor internalization, and identify the protein kinase(s) responsible for this phosphorylation, (3) To determine the role of src family kinases in the action of neurokine receptor signaling in the nervous system. Previous work has demonstrated that a number of src family kinases are associated with the activated LIF receptor, and we have found that that src kinases are activated following LIF stimulation of both neuronal cell lines and cultured neurons. This proposal will determine the role of src family kinases in neurokine action in neuronal cells. The research described here should provide new information on the function and regulation of the neurokine receptors and on the molecular basis for their diverse actions in the nervous system.